Schoeps Mikrofone CMC 6 Microphone Amplifier

The capsules of condenser microphones can't be connected directly to microphone cables or inputs; a microphone amplifier is required in between. Thus a complete microphone of the Colette series comprises any of the twenty available types of capsules combined with an amplifier. The CMC 6 U is designed for standard 48- and 12-Volt phantom powering. Its circuitry recognizes the supply voltage and adjusts itself automatically. Its performance characteristics remain essentially the same either way; mainly, the difference is that the current drawn at 12 Volts is greater than at 48 Volts. However, the 12-Volt mode consumes less power and might be preferred for battery-powered recording.

The microphone amplifier is responsible for providing the necessary electric charge to the capsule, without which it would be unable to generate a signal. Since the capsule's output signal is very weak (Hi-Z), it must be amplified. In order for the microphone's output to cleanly reach the next stage in the signal chain, it must undergo balancing and impedance matching before transmission. The CMC 6 incorporates a balanced, direct-coupled class-A amplifier, yielding a low output impedance, high RF shielding, and minimal distortion.

Features

The CMC 6 is our most popular amplifier. Its electrical properties have set new standards in terms of low distortion levels and common mode rejection (i.e. suppression of interference induced in the microphone cable).

• Flat frequency response
• Very low harmonic distortion and noise
• Balanced, low-impedance output
• High suppression of interference on the microphone cable
• Excellent protection against high-frequency radio interference with "RFI Shield"
• Frequency-independent impedance
• Signal transmission possible over very long cables
• Reliable operation even with weak phantom power
• Symmetrical, transformer- and capacitor-free output stage with a class-A amplifier
• Above 20 kHz, the signal is attenuated for protection against interference in the ultrasonic range, e.g. through the ultrasonic autofocus of a film camera

Specifications

Maximum sound pressure level (THD < 0.5 %) - with MK 4: 131 dB-SPL (P48, P12)

Frequency range - 20 Hz - 20 kHz

Sensitivity - see corresponding capsule

Maximum output voltage - 1 V (0 dBV) with 1 kΩ load

Low cut filter - 20 Hz, 12 dB/oct.

Minimum recommended load impedance - 1 kΩ

Output impedance - 42 Ω

Maximum cable length - > 400 m / ~1300ft

SCHOEPS RFI Shield - Yes

Powering standard / Valid range - P48 / 20-52 V

                                                          P12 / 10-13 V

Current consumption - 4 mA (P48)

                                      - 8 mA (P12)

Common mode rejection ratio (at 1 kHz) - > 55 dB

Output - XLR-3M, analog, 1 channel

• Length - 116 mm / ~4,5"
• Diameter - 20 mm / ~0,8"
• Weight - 60 g / 2,1 oz

Surface finish - Matte grey

                         - Custom colour: nickel, chromagreen

Variants & Options

• No. 191102 custom colour: nickel, chromagreen, other custom colours on request
  
• No. 191201 custom engraving
• Apart from the standard CMC 6 version, Special versions of the CMC 6 U are available.
• CMC 6 U linear

The CMC 6 U microphone amplifier normally has a gradual rolloff in response below 20 Hz to guard against infrasonic disturbances from various sources such as air movement and vibration. However, when using pressure (omnidirectional) transducers, particularly with digital recording, it can be desirable to pick up frequencies below 20 Hz without attenuation. The special technology of the CMC 6 U linear microphone amplifiers makes this possible; on request we can deliver microphone amplifiers with response that is flat to as low as 10 Hz. Caution must be advised with respect to infrasonics, however. Since pressure transducers can pick up very low frequencies, ventilation systems in large spaces (churches, concert halls) or traffic rumble can create a problem. With pressure gradient transducers the risk is even greater. They are far less sensitive to very low frequency sound, but respond much more strongly to low-frequency mechanical stimuli such as air currents and solid-borne noise. Such signals may be below the audible range of frequencies, but they can overload electronic circuitry and produce severe distortion, particularly in transformer-coupled circuitry.

CMC 6 U +5 dB

The sensitivity of a microphone using this type of amplifier is 5 dB higher than with the standard version, but the equivalent noise level and maximum output voltage are not materially affected. Thus the highest sound pressure level which the microphone can accept without distortion is 5 dB lower than in the standard version, while the signal-to-noise ratio is essentially the same with either gain setting. This version might be chosen in order to raise the microphone's signals above the noise level of the equipment to which it will be connected, and / or for working with sounds that occur mainly at low levels.

CMC 6xt U – the 40 kHz version